Other approaches to study natural selection





Museum specimens provide resource for comparisons over time, but many traits cannot be measured from specimens


What if researchers could have access live animals from a historical time point that had frozen in time?


For some species, seeds, eggs, cysts, spores can be preserved in soil or ice and revived years or even centuries later

Case study: Daphnia











Question: Can Daphnia evolve to cope with global warming?


Approach 1: Experimental evolution


Approach 2: Resurrection ecology


CTmax - upper threshold of temperature that an organism can function normally

Case study: Daphnia



Approach 1: Experimental evolution - Evolved Daphnia under control and warmed conditions for 2 years

Case study: Daphnia



Approach 2: Resurrection ecology - Hatched Daphnia from historic and contemporary sediment layers

















Conclusion: Thermal tolerance in Daphnia can evolve over short time scales in response to global warming

Case study: Daphnia can evolve….so what?



Daphnia not only interact strongly with its phytoplankton food resource, but also with other components of marine food webs

Current climate change threaten 16% of species with extinction


Can adaptation prevent extinction?



  • Evolutionary rescue? = process by which a population—that would have gone extinct in the absence of evolution—persists due to natural selection


  • So far, not been shown to be common in nature
    • cricket versus fly parasitoid


  • Experimentally - more common
    • yeast evolving to tolerate previously lethal salt concentrations


  • Can strong selection have risks?
    • can species adapt to multiple global change stressors?

Are there limits to adaptation?






Some organisms can adapt rapidly, but not always rapidly enough


What happens when the rate of environmental change exceeds the ability of populations to adapt?

Are there limits to adaptation?



Some organisms can adapt rapidly, but not always rapidly enough


For example, some populations do not have enough genetic variation to track forecast changes in climate


A 2°C rise in the next 60 years (12 birch generations) is predicted to advance budburst by 40 days


Billington & Pelham (1991) predicted how much change would need to occur per generation versus current population variation


Predicted change would be impossible

Traits that facilitate adaptation



Why can some species evolve quickly enough to cope with global warming while others can’t?


What traits make a species more likely to exhibit the adapt response?


BRAINSTORM: All else being equal, we expect higher likelihood of adaptation in organisms with…

Traits that facilitate adaptation






Higher trait heritability (for the relevant traits)


Adaptation cannot occur if a trait is not inherited


Heritability varies by trait

Traits that facilitate adaptation



More existing genetic variation (in relevant traits)


Adaptation from existing or “standing” genetic variation can be fast because the population does not have to “wait” for new mutations to occur.

Traits that facilitate adaptation



More existing genetic variation (in relevant traits)

Traits that facilitate adaptation



Contrast that with waiting for a new mutation

Traits that facilitate adaptation



Higher mutation rates


Faster mutation rates generate more variation on which selection can act

Traits that facilitate adaptation



Faster generation times


The relative velocity of environmental change is slower for organisms that can go through many generations each year

Traits that facilitate adaptation



Larger population sizes


Larger populations are more likely to have standing variation and are less likely to be decimated by chance events

Traits that facilitate adaptation



Other factors like amount of gene flow and how traits are linked to each other in the genome also matter

Microevolution: Rapid selection of tuskless female elephants


The survival of tuskless females across this 28-year period was estimated to five times that of tusked individuals in Gorongosa National Park (Campbell-Station et al. 2021)

Friday Discussion: Can Humans Adaptt to Global Change?



  • Do Humans have high adaptive capacity..


  • What evidence exists? Past, present and/or future
    • What adaptations have already occurred?
    • Do humans adapt easily?
    • Can/How/Will human adapt to 3-4C warming?


  • Be prepared to discuss what you found as well as your opinion on if it is possible


  • Submit an article/link on Brightspace for participation
    • Add a sentence or 2 about what you found